The present invention generally relates to air cleaners and, more particularly, to dynamic or centrifugal air cleaning systems for portable power tools.
In portable power tools, such as chain saws, blowers, string trimmers, and hedge trimmers, significant attention has been paid to methods for removing dirt and particles from ambient air prior to its introduction into the carburetor. Typically, such methods employ a filter media which traps and separates entrained particles from the air stream prior to introduction of the air into the carburetor. However, in dirty or dusty conditions, which is a common operating environment for portable power tools, the filter media quickly becomes saturated or clogged with filtered particles and tends to resist or impede air flow, leading to degradation of the power tool performance. Thus, the filter media must be periodically cleaned or replaced, and represents a serious problem to the operator from a stand point of convenience and down-time.
In response to this problem, air cleaning methods have been developed to take advantage of the centrifugal effects or forces present in an air stream flowing within a fan volute radially surrounding a fan or flywheel of the power tool. In this regard, it has been recognized that dirt or heavier-than-air particles tend to be entrained in the fastest moving portion of the air stream adjacent the radially outermost portion of the fan volute while the radially innermost portion of the air stream is relatively slower moving, and tends to be free of entrained particles.
One known centrifugal air cleaning method employs an air inlet tube having an inlet opening disposed Within the fan volute between the fan and a curved outer wall which defines the outermost extent of the volute. The inlet opening is disposed within the air flow path of the volute generally transverse to the direction of air flow and receives a radially-inward portion of the air stream flowing within the volute (i.e., the relatively slower-moving portion of the air stream). Since it is presumed that the majority of dirt and particles will be entrained in the radially outermost portion of the air stream flowing in the volute (i.e., adjacent the curved outer wall), the air entering the inlet opening should be relatively free of dirt. However, this presumption fails to account for the air with entrained dirt that flows radially outward from the fan, a portion of such radially-flowing dirt being directly introduced into the inlet opening of the air inlet tube and contaminates the carburetor.
Another type of centrifugal air cleaner is taught in U.S. Pat. No. 4,261,302, which shows an air inlet opening formed in a bottom wall of a fan housing. Upstream of the air inlet, an upwardly curved lip is provided to deflect dirt within the air stream upwardly and away from the air inlet. An upwardly sloping ramp downstream of the air inlet also diverts dirt away from the air inlet. However, the air cleaning system shown in the '302 patent does not provide means for preventing radially propelled dirt from reaching the air inlet port.
Therefore, there exists a need in the art for a device which takes full advantage of the centrifugal air cleaning ability available in portable power equipment while eliminating or removing the shortcomings of the presently known centrifugal air cleaning devices.